The present invention relates to an image encoding apparatus and image decoding apparatus.
Conventionally, an image encoding apparatus which encodes an image to decrease the data amount of a color image and an image decoding apparatus which decodes encoded image data are known, as disclosed in Japanese Patent Laid-Open Nos. 6-152985 and 6-14201.
In a conventional encoding scheme such as JPEG (Joint Photographic Experts Group) for a color image, quantization is performed to improve the compression ratio. However, block distortion may be generated, or edge business may occur at a line portion or a contour portion due to the quantization. This is because common quantization processing is executed for both an image region where a high resolution is necessary and an image region where a low resolution suffices without considering the image characteristic for each pixel. For example, when block encoding is employed, like T81 recommended by ITU (International Communication Union), if the compression ratio is increased, the image quality conspicuously degrades in a region such as a line portion or contour portion having a high spatial frequency.
In addition, for the conventional image encoding/decoding apparatus, although a technique of segmenting an image into objects in accordance with characteristics and compressing the image has been proposed, no detailed proposal has been made about an actual scheme for efficiently compressing a color line image.